The Brew Cabin

Posted: **Thu Feb 23, 2017 9:56 am**

Two years ago, we moved house. The place has over 260m2 of paved driveway, with a turning circle, put in about 20 years ago. When we arrived, many of the pavers around the turning circle were very loose and wobbly.

We had the pavers re-laid in the worst area, but they never bedded in properly. The sand disappeared from between the pavers within a couple of days. Brushing more sand in just caused a repeat of the problem and many of the pavers now rock from side to side when stood on. The guy who re-laid the pavers thought the problem may have been poor drainage, since we have clay soil, but he noted that it seemed odd, given that the site has a natural slope for water to run off.

We are now getting quotes to completely re-do the whole drive, using interlocking 50mm thick pavers. The paving guy who we are most likely going to get to do the job took the time to dig down under the pavers and found that in the spot he excavated in, there is only 100mm of sub-base and that the base seems to be in good condition. He thinks it should have been made 150mm - 200mm thick and that this may explain the ongoing problems.

He proposes scraping back the bedding sand, then adding an extra 50mm of sub-base on top, before laying the new interlocking pavers.

Does this sound like a reasonable approach and one that's likely to give a stable driveway that won't disintegrate?

Here are a couple of photos:

Posted: **Thu Feb 23, 2017 1:16 pm**

Seems you are losing the sand beteeen the sub base. 100ml dtp1 wouldn't cause the sand to dissapear and is good enough for light vehicle use. What type of sub base is under the bedding? Could be no fines sub base.

Posted: **Thu Feb 23, 2017 6:29 pm**

Like Sean, I don't think it's a sub-base problem, at least, not a sub-base depth problem, I'd be more interested in looking at the bed sand. If that is pumping-up via the joints, then either it's the wrong sand or it's degraded to the point at which it's useless.

How does your man plan to add 50mm of sub-base? It would elevate the repaired area, compromising threhold levels and, possibly, breaching DPC levels. And to add 50mm, he'd need to loosen at least 50mm of the existing sub-base, mix in the new stuff to get proper integration, then re-compact. Also note that the bed sand *cannot* be re-used.

For me, there's little point in re-laying until the cause of the problem is identified, and that, I suspect, can only be done by a careful assessment by someone with pavement engineering experience.

Posted: **Thu Feb 23, 2017 9:38 pm**

Is the paving bedded on sand or stone dust.
I've seen this problem of wobbly blocks most often when bedded on stone dust. It's used as it's cheaper than sand but the flexibility gets lost after time as it sets like concrete and any minor deviations will cause rocking, wobbling even rattling as you drive over them.

As above, it's not a base problem and would leave well alone unless there are many ruts and divots.

Posted: **Fri Feb 24, 2017 7:55 am**

Thanks for taking the time to respond.

I think the plan is to bring an excavator in and just remove the bedding sand, before compacting the extra base on top. There wasn't any mention of mixing the new base in with the old.

The extra 50mm is not likely to cause problems. The drive is surrounded by a box hedge (75m of it!), so the hedge should hide the drop off at the edges and over time, we'll build the ground up with compost and pine bark.

Some of the worst parts are in locations where drivers are turning the steering wheel from lock to lock - e.g. backing out of the garage and turning around the turning circle. I'm hoping that using interlocking pavers might help stop any lateral movement.

I did a bit of digging under a loose paver tonight. There's some fine sand, then a layer of fairly coarse sand. Below that, very hard, tightly compacted "road base" as we call it here. I can see bits of blue metal with some sort of sand around it. My trowel and an old screwdriver didn't make much of a dent in it. If it helps, here are a couple of photos - the first taken straight after the paver was lifted:

Posted: **Fri Mar 03, 2017 4:03 am**

Shred wrote:I'm hoping that using interlocking pavers might help stop any lateral movement.

On it's own, horizontal interlock is not enough.

You need really sound edge restraints and millimeter-perfect cutting-in, along with tight, well-filled joints and that will prevent any lateral movement.

I've seen dozens, possibly hundreds, of jobs where blocks laid as herringbone with what is assumed to be full horizontal interlock have failed, and failed disastrously in some cases (yes: Brisdge St in Warrington was a classic example!)

In every case, the failure was due to one or more of:

1 - failed edge restraints
2 - poor quality cutting-in
3 - loose-laid blocks

....and of these, by far the most common was poor cutting-in.

The Brew Cabin

Loose pavers - won't bed in